This application is for the Coordinating Center of a national collaborative randomized controlled clinical trial of photocoagulation treatment for central vein occlusion. The study will be conducted in nine clinical centers, with the Reading Center at the Bascom Palmer Eye Institute (University of Miami) and the Coordinating Center at Scott and White Hospital in Temple, Texas (Texas A&M University). Patients will be entered into four study groups: Nonperfused (Group N); Macular Edema (Group M); Perfused (Group P); and Indeterminant (Group I). Eyes in the first two groups will be randomly assigned to photocoagulation treatment and a control group. Patients in groups P and I will be followed for natural history and for possible later entry into the randomized study. Projected recruitment is 792 patients: 238 in in Group N; 396 in Group P and 158 in Group I. About half of these patients will also be in Group M. Patients will be recruited for the first three years of this five year study and all patients will be followed for three years or until termination of the study. The study is designed to provide information regarding whether or not photocoagulation is efficacious in preventing neovascularization and subsequent neovascular glaucoma in eyes with central vein occlusion and retinal ischemia and whether or not photocoagulation treatment is useful in preserving visual acuity in eyes with CVO and macular edema. Information collected at baseline and each follow-up visit will be forwarded to the Coordinating Center for processing and analysis. A data monitoring committee will review interim results of the study every six months.